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/*
* Routine to disable IP-level socket options. This code was taken from 4.4BSD
* rlogind and kernel source, but all mistakes in it are my fault.
*
* Author: Wietse Venema, Eindhoven University of Technology, The Netherlands.
*/
#ifndef lint
static char sccsid[] = "@(#) fix_options.c 1.6 97/04/08 02:29:19";
#endif
#include <sys/types.h>
#include <sys/param.h>
#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netdb.h>
#include <stdio.h>
#include <syslog.h>
#ifndef IPOPT_OPTVAL
#define IPOPT_OPTVAL 0
#define IPOPT_OLEN 1
#endif
#include "tcpd.h"
#define BUFFER_SIZE 512 /* Was: BUFSIZ */
/* fix_options - get rid of IP-level socket options */
fix_options(request)
struct request_info *request;
{
#ifdef IP_OPTIONS
unsigned char optbuf[BUFFER_SIZE / 3], *cp;
char lbuf[BUFFER_SIZE], *lp;
int optsize = sizeof(optbuf), ipproto;
struct protoent *ip;
int fd = request->fd;
unsigned int opt;
int optlen;
struct in_addr dummy;
if ((ip = getprotobyname("ip")) != 0)
ipproto = ip->p_proto;
else
ipproto = IPPROTO_IP;
if (getsockopt(fd, ipproto, IP_OPTIONS, (char *) optbuf, &optsize) == 0
&& optsize != 0) {
/*
* Horror! 4.[34] BSD getsockopt() prepends the first-hop destination
* address to the result IP options list when source routing options
* are present (see <netinet/ip_var.h>), but produces no output for
* other IP options. Solaris 2.x getsockopt() does produce output for
* non-routing IP options, and uses the same format as BSD even when
* the space for the destination address is unused. The code below
* does the right thing with 4.[34]BSD derivatives and Solaris 2, but
* may occasionally miss source routing options on incompatible
* systems such as Linux. Their choice.
*
* Look for source routing options. Drop the connection when one is
* found. Just wiping the IP options is insufficient: we would still
* help the attacker by providing a real TCP sequence number, and the
* attacker would still be able to send packets (blind spoofing). I
* discussed this attack with Niels Provos, half a year before the
* attack was described in open mailing lists.
*
* It would be cleaner to just return a yes/no reply and let the caller
* decide how to deal with it. Resident servers should not terminate.
* However I am not prepared to make changes to internal interfaces
* on short notice.
*/
#define ADDR_LEN sizeof(dummy.s_addr)
for (cp = optbuf + ADDR_LEN; cp < optbuf + optsize; cp += optlen) {
opt = cp[IPOPT_OPTVAL];
if (opt == IPOPT_LSRR || opt == IPOPT_SSRR) {
syslog(LOG_WARNING,
"refused connect from %s with IP source routing options",
eval_client(request));
shutdown(fd, 2);
return;
}
if (opt == IPOPT_EOL)
break;
if (opt == IPOPT_NOP) {
optlen = 1;
} else {
optlen = cp[IPOPT_OLEN];
if (optlen <= 0) /* Do not loop! */
break;
}
}
lp = lbuf;
for (cp = optbuf; optsize > 0; cp++, optsize--, lp += 3)
sprintf(lp, " %2.2x", *cp);
syslog(LOG_NOTICE,
"connect from %s with IP options (ignored):%s",
eval_client(request), lbuf);
if (setsockopt(fd, ipproto, IP_OPTIONS, (char *) 0, optsize) != 0) {
syslog(LOG_ERR, "setsockopt IP_OPTIONS NULL: %m");
shutdown(fd, 2);
}
}
#endif
}
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